Kuraray Noritake Newsletter Vol.1

BOND NEWSLETTER FOR PROFESSIONALS IN DENTISTRY

VOLUME 1 | 12/2016

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90 years of Kuraray a glimpse of the history

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Functional monomer research.

Report of ACTA Congress

Strong, stronger, strongest.

Cementation of zirconia BOND

Bolle Exhibition Centre, Grappa Nardini, Bassano del Grappa, Italy Glass types: 2,000 units of insulation glazing and float glass with TrosifolÂŽ film, 45 mm thickness per glazing unit.

90 years of Kuraray a glimpse of the history Kuraray will be celebrating its 90th anniversary this year. We take the opportunity of this occasion to offer you a glimpse of the history of Kuraray from a new perspective. The name Kuraray represents more than 8,300 employees and an annual turnover of approximately 3.7 billion euros. Kuraray was founded in Kurashiki, Japan, in June 1926, by Magosaburo Ohara. Kuraray began with the domestic production of Rayon, a synthetically produced cellulose fibre referred to as artificial silk, a new and innovative product at the time.

The founder of Kuraray Magosaburo Ohara 4

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The name KURARAY is derived from the location: Kurashiki and the product manufactured: Rayon.

The development of this branch of production developed very quickly in Japan, with many other major manufacturers establishing themselves during this period. Whereas others recruited their technicians and experts from elsewhere, Kuraray established the Kyoko Research Laboratory, which was managed by the University of Kyoto to generate expertise and support for the development of the required technologies.

Ohara also committed himself to cultural and social projects. The building of an art gallery and the financing of an orphanage represent only two of his many projects in Kurashiki. The Ohara Museum of Art was the first private museum of Western art in Japan.

Ohara considered the dreadful conditions in which employees commonly worked and lived at the time to be unacceptable; he was not a profit-driven employer, and attempted to solve such issues. He ensured that decent accommodation,

fitness facilities and nursery schools were built to provide young employees, or families who had left their homes to work for Kuraray, with everything they needed for education and a healthy and culturally rich lifestyle.

One of the largest general hospitals in the west of Japan, the Kurashiki Central Hospital, was originally founded by Kuraray to promote the well-being of employees and their families. It is still considered to be one of the most famous hospitals in Japan.

With the production of Kuralon in 1950, developed from the in-house manufactured products PVA and vinyl acetate, Kuraray expanded to become the specialist chemical company it is today.

Always intent on making a contribution to the good of society, Kuraray addressed the subject of environmental protection very early on. The visionary Ohara was aware of the seriousness of environmental pollution, and made great efforts to prevent it.

Internationally too, Kuraray has remained aware of its social responsibilities. After the war, a production facility was opened in China which helped to improve the poor post-war living conditions of the Chinese population.

Today, Kuraray is a leading global manufacturer of the specialist chemicals used in many aspects of daily life. Kuraray has always viewed its employees as its most important asset, and continues to do so to this day.

The Ohara Museum of Art in Kurashiki

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MDP since 1981

What if Kuraray Noritake Dental had not developed the MDP monomer?

What would the quality of adhesive dentistry be if Kuraray Noritake had not developed the MDP monomer? MDP has proved to be a very effective functional monomer for creating durable bonding to enamel, dentine and metals. The best-known products containing MDP are CLEARFILTM SE BOND and PANAVIATM. Structure of Adhesive monomer MDP

CH3

Polymerisable group (1)

CH2 = C C =O O CH2

CH2

CH2

CH2

CH2

Hydrophobic group (2)

CH2

CH2 CH2

CH2

CH2 O

O = P OH OH

Hydrophilic group (3)

Forming the chemical bond with calcium in hydroxy apatite

Fig. 1 The chemical structure of adhesive monomer (MDP)

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Adhesion to various substrates is possible Thanks to MDP (methacryloyloxydecyl dihydrogen phosphate), which has been shown to create a long term, durable and stable bond to both dental tissue and metal oxides. Research conducted over the past few decades has demonstrated the effectiveness of MDP. The first Kuraray Noritake Dental product to contain MDP was PANAVIA EX. Various other adhesive and cementation systems followed. Our latest products, PANAVIATM V5 and CLEARFILTM Universal Bond, also rely to a large extent on the performance of the original MDP monomer. MDP has the following structure: 1. t erminal double bond group for polymerisation 2. hydrophobic alkylene group to maintain a delicate balance between hydrophobic and hydrophilic properties and 3. hydrophilic phosphate group for performance of the acid demineralisation and chemical bonding to tooth structure.

History In the years between 1978 and the late 1990s, it became possible to increase the bond strength to dentine to more than the intrinsic strength of the dentine itself. MDP played a major role in these developments. The solid ionic bond with calcium from the HAp in dental tissue means that such failures as occur are cohesive in the dentine rather than being failures of the adhesive. Apart from in vitro studies confirming this bond strength, the long term clinical durability recorded over 13 years is also impressive.

Research Research from Yaun et al., 2007, shows that defects along the interface are largely responsible for degradation of the hybrid layer. CLEARFILTM SE BOND exhibited no such defects. So it was expected that SE BOND would also prove to have a stable connection to dental tissue. Recently, Peumans et al. From Leuven University, Belgium found CLEARFILTM SE BOND to still have excellent clinical effectiveness after 13 years.

In their publication in the Journal of Dental Research 83, 2004, Yoshida et al. concluded that the choice of the adhesive monomer played a significant role in the effectiveness

of the adhesive. They found MDP to be the best and fastest in tests for chemical adhesion (ionic bonding) and stability in a moist environment (insoluble) – better and more stable than 4-MET and Phenyl-P, in that order.

After 35 years, MDP is still in a class of its own. To date, no manufacturer has been able to develop an adhesive monomer with better adhesion properties combined with durable bond strength. Many attempts have been made, but none have succeeded. In the meantime, Kuraray’s patent on MDP has expired. This has opened up the market for other manufacturers to synthesise their own MDP. Only a few non-dental chemical

companies are supplying MDP to other manufacturers of adhesive systems, and the synthesis of high-purity MDP remains extremely difficult.

More recently, Kumiko Yoshihara et al. published ‘Functional monomer impurity affects adhesive performance’, in Dental Materials 31 (2015) 1493-1501. They concluded that the three MDP’s they studied exhibited different levels of purity.

Differences in the resultant hybrid layers were observed in all three MDP versions: both impurities and the presence of dimers had an effect on the etching efficacy of the HAp, and also on the intensity of nano-layer presence and the immediate bond strength.

µTBS of MDP’s from different origin

Yoshihara Ket al. Functional monomer impurity affects adhesive performance Dent Mater 31, 1493-1501, 2015

EXPLANATION

20 24 HOURS TC 100.000

MPa

15 10 5

The three 10-MDP’s studied in this study clearly revealed a different purity.

Differences in the ultrastructure of the resultant hybrid layers were observed for the three 10-MDP versions. Both the impurities and the presence of dimers affected the etching efficacy of HAp, the intensity of nano-layering and the ïmmediate’ bond strength .

QUOTE

0 10-MDP KN 10-MDP PCM 10-MDP DMI

The purity of 10-MDP present in commercial dental primers, adhesives and cements can be expected to influence bonding performance.

KN: KURARAY NORITAKE JAPAN PCM: PCM GERMANY DMI: DMI USA

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Strong, stronger Functional monomer research

Following the success of CLEARFIL BOND SYSTEM F, a new R&D goal was set: to develop a monomer that performed better than Phenyl-P, making it possible to achieve higher bond strengths and longer-lasting composite restorations as a result. To begin with, the chemical composition of Phenyl-P was analysed in depth. Each of the three main components of this functional monomer – in other words the polymerisable group, spacer and reactive group – was then studied in detail (see Fig. 1).

Chemical structure of adhesive monomer CH₃ O =

CH₂=C ①Polymerizable group

—

COOCH₂CH₂O — P —O— ②Spacer

OH

Fig. 1 The chemical structure of adhesive monomer (Phenyl-P）

③Reactive group

One study involved changing the length of the spacer while keeping the other components the same. This demonstrated that the length of the spacer clearly influenced the bond strength to human dentine and Ni-Cr alloy. A similar test was carried out by exchanging just the reactive group (Fig. 2 and 3). These studies (Fig. 4) gave valuable insights into the ideal functional monomer. The results from our countless tests were as follows: T he spacer must be a hydrophobic group with 4 or more carbon atoms.

■ The reactive group must be a divalent phosphate group.

■ There must be a radical polymerizable group.

■

Applying all these lessons to hundreds of functional monomer variations led to the development of a functional monomer still in use today: Methacryloyloxydecyl Dihydrogen Phosphate (MDP). We like to call it ‘The Original MDP Monomer’.

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CH₃

O

=

CH₂=C

COO ‒CH₂ ‒O‒P‒ OH n OH —

10

CH₂=C

CH₃

O

=

5

COO ‒CH₂ ‒O‒P‒ OCH₃ n OH —

Strength of the bond to human dentin（MPa）

Effect on the bond strength to dentin

0

2

8 6 Spacer length

4

10

Fig. 2 Optimizing the chemical structure of the adhesive monomer

Number of carbon atoms

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60

CH₃

O

=

CH₂=C

COO ‒CH₂ ‒O‒P‒ OH n OH —

40

CH₂=C

CH₃

O

=

20

COO ‒CH₂ ‒O‒P‒ OCH₃ n OH —

Strength of the bond to Ni-Cr alloy（MPa）

Effect on the bond strength to Ni-Cr alloy

0

2

4

6 8 Spacer length

10

12

Fig. 3 Optimizing the chemical structure of the adhesive monomer

Number of carbon atoms

The Chemical structure of the reactive group

COOH

Impact of the polymerisable group on metal adhesion

COOH

—

O

— ≧ — O — P — OR

OH

—

—

—

OH

OH

OH

=

> —

—

—

COOH

＞ —

COOH

—

OH

OH

—

—

=

Ni-Cr O alloy — O — P — OH ≧ —

COOH

—

OH

≧ —

—

=

—

COOH

— O — P — OH ≧ — O — P — OR ≧ —

—

=

O

O

—

Dentin

> — O — S O（ 2 OH）

OH

CH₂=C

CH₃

CH₃

COO —

COO —

＞＞ CH₃ — CH

Fig. 4 Optimizing the chemical composition of an adhesive monomer

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The adjacent teeth were separated by means of a transparent strip, after which the preparation was etched with 35% phosphoric acid (picture 7). TOOTH PRIMERTM was applied after thorough rinsing with water and drying after it had taken effect for 20 seconds.

A thin layer of PANAVIATM V5 cement was then applied to the facing.

The facing was placed on the preparation with the application of light finger pressure. A microbrush was used to remove the major excess along the margins. The cement of the buccal and palatal aspect was light cured for 5 seconds. A sharp scaler and floss were used to remove the final excess. Glycerine gel was then applied to the outline to avoid oxygen inhibition during curing. The cement was finally light cured from both sides for 20 seconds, the glycerine gel was rinsed away and the margins were finished by means of a composite polishing stone. After placement of the first facing, the rubber dam clamp was moved to the neighbouring tooth so the cementation of the second facing could proceed. This facing was once more tried for fit, pre-treated and cemented in an identical manner (picture 8).

The result The facings were checked a few weeks later (picture 9). Joris was very satisfied with the aesthetics of his two central incisors. The transitions from tooth to restoration were invisible and the gingiva was healthy.

10 The transparency, surface structure and gloss are better adjusted

to the neighbouring elements and to Joris’s smile (picture 10).

Dentist: Paul de Kok, Amsterdam Periodontics Clinic Dental technician: Eric van der Winden, Oral Design Center Holland

PAUL DE KOK USED CLEARFILTM CERAMIC PRIMER PLUS AND PANAVIATM V5 FOR HIS CASE STUDY

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Shear bond strength (MPa)

50 40

43.8

30

31.2 25.2

20 10 9.7

0

Panavia V5

RelyX Unicem 2 Automix1

RelyX Ultimate1

Multilink Automix1

(MPa) 30 37OC, 24 UUR TC3000

25 20 15 10 5 0

HPC-100

RelyX Ultimate1

Multilink Automix1

RETENTION RATE AFTER 13 YEARS ClearfilTM SE BOND (selective enamel etch) ClearfilTM SE BOND

Retention Rate %

100 80 60 40 20 0

5 YEARS

8 YEARS

13 YEARS

should be so wide that customised solutions can be realised.

Among other things, he believes that there will still be room for baked porcelain on a core of lithium disilicate or zirconia. Using baked porcelain, the dental technician can modify the surface texture of an aesthetic restoration to lend, as it were, a certain age to the restoration.

As for surface structure, the fact that the material allows for the smooth polishing of the occlusal plane is crucial to counteract abrasion by the antagonist and to maintain the occlusal balance.

In this respect, the hardness of the material selected is not the main factor; the smoothness and resistance of the surface are far more important.

These veneers were made from KATANATM Zirconia UTML and coloured using CERABIENTM ZR External Stain

has become a thing of the past; full-ceramic materials are now the standard. Zirconia still has a relatively poor reputation in terms of aesthetics due to the extreme whiteness of the earliest examples from the turn of the century. Types of zirconia are now available with varying translucencies, and there are even socalled multi-layer varieties (KATANATM Zirconia ML, STML and UTML by Kuraray Noritake), and these new zirconia no longer have to be porcelain-baked. Obviously, baking is still possible, and partial baking is a choice that is frequently made. One of the results of a multi-layer build-up is that the transparency is higher incisally than cervically, as it is in natural elements; the light falls through the incisal margin, but is blocked at the cingulum of the restoration. With a modern zirconia material such as KATANATM Zirconia ML, this variable transparency goes hand in hand with a natural colour gradient from cervical to incisal. In a given colour, A1 for example, the cingulum has the corresponding dentine shade body and it passes to incisal in the appropriate enamel colour via two transition shades.

FLEXURAL STRENGTH When selecting material for restorations, the dental technician also has the option to choose KATANATM Zirconia Ultra Translucent Multi-Layered for veneers or anterior crowns; a zirconia with a translucence comparable to that of glass. This translucence is especially important with anterior restoration which is to be fitted between flawless natural elements, a situation that often occurs after anterior traumas. Such a restoration effected using KATANATM Zirconia UTML harmonises with the neighbouring natural teeth, not least because this type of zirconia does not cause the frequently-occurring white appearance common in anterior crown. The modern aesthetic zirconia materials of the second generation are sintered at a temperature of 1,550°. This temperature is maintained for two hours. The dental technician needs to be aware that this temperature differs from the sintering temperature for KATANATM Zirconia High Translucent MultiLayered (1,500 °C). Wide-span bridges can be realised with the latter product, whereas the size of bridges made from KATANATM Zirconia Super Translucent Multi-Layer remains limited to a maximum of four elements. KATANATM Zirconia UTML can be used for small anterior bridges, but is more suitable for anterior crowns and veneers. The reason for this is that the flexural strength of these highly aesthetic zirconia materials is lower than the flexural strength of the standard zirconia, in which the flexural strength

SURFACE The new zirconia materials are changing the way dental technicians operate, as illustrated by the experience of Daniele Rondoni, a renowned dental technician. This professional, from Savona in Italy, has specialised in the use of Multi-Layering technology for ceramic materials (Tecnica della Multistratificazione in Ceramica).

According to his philosophy, the choice of restoration materials

Minimum wall thickness of KATANATM

UTML

STML 1,0 mm 0,4 mm

0,8 mm

0,8 mm 0,8 mm

1,0 mm

0,8 mm

1,0 mm

1,0 mm

1,0 mm

1,0 mm

1,0 mm

1,0 mm 1,0 mm

1,0 mm

1,0 mm

1,0 mm

0,4 mm 0,8 mm

Anterior crown

0,4 mm

Veneer

Posterior crown

Inlay

* Maintain 0.8 mm thickness of pressed ceramic in all areas.

When trimming of the zirconia framework the framework should be at least 0.4 mm.

Onlay

ML & HT 0,5 mm 0,4 mm 0,4 mm

0,5 mm

0,5 mm

0,5 mm

0,5 mm

0,4 mm

0,4 mm 0,4 mm

0,5 mm

0,5 mm

0,5 mm

0,5 mm

0,5 mm

0,5 mm

0,4 mm 0,4 mm

0,4 mm

Anterior crown

Veneer

Posterior crown

Inlay

Onlay

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It’s time to support your science We would like to introduce you to our European Scientific Team. Each year, we support universities with products for research or ask universities to conduct in vitro or in vivo analysis of our products. We currently have more than 12 commissioned studies of one of our new products in progress at various European universities. The Kuraray Noritake company appreciates every effort made in studying Kuraray products to confirm their quality or to indicate room for improvement.

Our European head office is located in Hattersheim, near Frankfurt in Germany, and it is from there that we support the technical managers of our subsidiaries, as well as European universities. Have you ever wanted to visit our company or talk to a member of our R&D team? This may well be your chance. Our current technical team consists of various Japanese and European members. If you would like to contact our technical team, please refer to the contact information provided below.

Each year, we provide free materials for research and student projects.

If you would like to known whether you might benefit from our scientific programme, please feel free to contact us to establish how we could help you and what information you will need to supply.

And that is not all. Starting this year, we will be gradually opening up our online database of product information. Here you will be able to find presentations, photos etc. for free downloading and sharing. We are going to begin with our latest introduction – PANAVIATM V5. Just send us an e-mail expressing your interest and you will be among the first to be invited.

You can contact us by sending an e-mail to science@ kuraraynoritake.com.

We look forward to hearing from you!

Mitsuru Takei Head of Technical Services

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